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Skeletal system (Vertebrae (defects (half a vertebrae missing (scoliosis),…
Skeletal system
Vertebrae
form from sclerotome part of somites
week 4
sclerotome cells migrate around
spinal cord
notochord
merging with the opposing side somite
resegmentation of the sclerotome
half of each sclerotome fuses with the subjacent sclerotome
myotomes bridge the intervertebral discs
movement
myotome derived from the somite
mesenchymal cells between segments
DO not proliferate
fill the space between two pre-cartilaginous vertebral bodies
formation of intervertebral disc
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patterning of the shapes of the different vertebrae
HOX genes regulate
vertebrae formation
two curves
primary curves
thoracic
sacral
secondary curves
cervical
child learns how to hold up her head
lumbar
forms while child learns how to walk
defects
half a vertebrae missing
scoliosis
number of vertebrae alternates
fused cervical vertebrae
reduced mobility and short neck
imperfect fusion of vertebral arches
involve only the bony vertebral arches
spinal cord left intact
spina bifida occulta
spina bifida cystica
Development
mesodermal germ layer
thickens and differentiates into
paraxial mesoderm
WEEK 3: begins to organize in segments
somitomers
(head region)
cephalocaudal formation
organize to balls of fibroblast-like cells
from the occipital region
development into somites
timing
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segmentation clock
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sophisticated somite differentation
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intermediate mesoderm
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connects lateral and paraxial
gives rise to urogenital structures
lateral plate
parietal mesoderm
lines the intraembryonic cavity
together with overlying ectoderm
lateral body wall folds
closes the ventral body wall
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forms
serous membranes, which will line
peritoneal cavity
pleural cavity
pericardial cavity
secretes serous fluid
sclerotome cells migrate
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forming
costal cartilages
limb muscles
most body wall muscles
visceral mesoderm
surrounds the organs
thin serous membrane around organs
together with embryonic endoterm
forms the wall of gut tube
layers line a newly formed cavity
intraembryonic cavity
each side of the embryo
neural crest
differentiate into
mesenchyme
formation of
facial bones
intramembranous ossification
skull
derived from occipital somites
Skull
divided in two
neurocranium
two parts
membranous part
flat bones
surrounding the brain
at birth
separated from each other by narrow seams of CT
remain membranous
some are open until adulthood
derived from
neural crest cells
paraxial mesoderm
intramembranous ossification
bone-like spicules
enables enlargement of the skull
membranous bones enlarge by apposition of new layers on the outer surface and demolishing the inside parts
cartilaginous part
forms bones of the base of the skull
endochondral ossification
viscerocranium
forms skeleton of the face
HEAD GROUP COVERS
skeletal development regulators
FGFRs
mutations (even point mutations) have been linked into
craniofacial defects and skeletal dysplasias
Cranioschisis
cranial vault fails to form
brain tissue exposed to amniotic fluid
degenerates brain tissue
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cranial meningocele
meninges and/or brain tissue herniates
may be treated succesfully
craniosynostosis
early closure of the sutures
most common causes are genetic
causes
teratogen exposion
low vitamin D
intrauterine constrains
multiple birth pregnancy
low amount of amniotic fluid
skeletal dysplasia
achondroplasia
large head
short extremities
short fingers
protruding abdomen
cleidocranial dysostosis
delayed closure of fontanelles, and sutures
clavicles underdeveloped or missing
teeth formation defects
FGFs
SIGNALING VIA
tyrosine kinase receptores
Sternum
develops independently in the parietal layer
sternal bands formed
on both sides of the midline
fusing together
forming cartilaginous model for sternum structure
in the ventral body wall
Ribs
derived from sclerotome
costal cartilage formed by sclerotome cells
migrate over lateral somitic frontier
to lateral plate mesoderm
